Seriously, people in the 14th century already KNEW the earth was round. Sure, they thought the sun orbited the earth, but they didn’t think the earth was flat.

Eratosthenes of Cyrene calculated the circumference of the earth and the tilt of the earth’s axis in the second century BC.

In the 14th century they were using calculations of the earth’s circumference that Ptolemy made in the second century AD. They were moderately inaccurate, but the errors weren’t really noticed until the 16th century.

Contrary to popular belief, people in the time of Columbus didn’t think the earth was flat either. His dispute with the church was about the diameter of the earth, not the shape of it. And Columbus was wrong. That’s why native Americans ended up being called Indians. Columbus got himself very, very lost and thought he’d found a new trade route to India.